The effect of manure on ammonia (NH3) emission was assessed with the manure in a deep pit and the manure on a partly slatted floor in a commercial fattening pig house. The manure in the pit was measured with its depth. The manure on the floor was determined with floor contamination that was the proportion of the floor surface covered by a mixture of urine and faeces. Ammonia emission from an exhaust chimney was continuously measured for 135 days with a NOx analyser and a full-size ventilation rate sensor. Measurement data were processed and 900 steady-state data subsets were extracted. The steady-state data were used to investigate the effect of manure on the NH, emission. There was no good relationship established between the NH3 emission rate and the manure depth (correlation coefficient r = - 0.143). However, the NH3 emission rate had a high correlation coefficient (r = 0.852) with the floor contamination. A linear equation was built for the relationship between the NH3 emission and the floor contamination. it was further found that the floor contamination itself was influenced by the weight of pigs and the inside room temperature. A model was developed to calculate the floor contamination as a function of the weight of pigs and the inside temperature (R-2 = 0.811). With higher floor contamination values in the house, the ventilation rate and the inside room temperature had stronger influence on the NH3 emission rate. (C) 1999 Elsevier Science B.V. All rights reserved.